The present invention relates to a process for the preparation of a 4,5-diamino shikimic acid derivative of formula
and pharmaceutically acceptable addition salts thereofwherein    R1, R1′ are independent of each other H or alkyl,    R2 is an alkyl and    R3, R4 are independent of each other H or an alkanoyl, with the proviso that not both R3 and R4 are H.
4,5-diamino shikimic acid derivatives of formula I, especially the (3R,4R,5S)-5-amino-4-acetylamino-3-(1-ethyl-propoxy)-cyclohex-1-ene-carboxylic acid ethyl ester and its pharmaceutically acceptable additional salts are potent inhibitors of viral neuramimidase (J. C. Rohloffet al., J. Org. Chem. 63, 1998, 4545-4550; WO 98/07685).
The problem at the root of the present invention is to provide a new process for preparing 4,5-diamino shikimic acid derivatives in good quality and yield from a easily obtainable starting material, 5-amino-shikimic acid. 5-amino-shikimic acid can be easily obtained from biotech processes, e.g. genetic engineering, fermentation (Jiantao Guo and J. W. Frost, Organic Letters, Vol. 6, No. 10, 2004, 1585-1588).